1. Field of the Disclosure
The present disclosure relates to an organic light-emitting diode display device, and particularly, to an organic light-emitting diode display device in which the number of signal lines is minimized by sharing a predetermined signal line between adjacent pixels in a display panel having a plurality of signal lines formed therein, thereby improving an aperture ratio.
2. Description of the Conventional Art
Flat panel displays as substitutes for existing cathode ray tubes are a liquid crystal display device, a field emission display device, a plasma display panel device, an organic light-emitting diode display device, etc.
Among these flat panel displays, the organic light-emitting diode display device has characteristics of high-luminance and low operating voltage. Since the organic light-emitting diode display device is a self-luminescent display device that emits light by itself, its contrast ratio is high, and the implementation of an ultra-thin display is possible. Since the organic light-emitting diode display device has a response time of about a few microseconds (μm), the implementation of moving images is easier than that in the liquid crystal display device. Further, the organic light-emitting diode display device has no limitation of viewing angle, and is stable even at a low temperature.
In a typical organic light-emitting diode display device, one pixel includes at least two switching and driving transistors, a capacitor and a light-emitting diode. The switching transistor applies a data voltage corresponding to the gray scale of an image to a gate of the driving transistor, and the driving transistor supplies current to the light-emitting diode according to the data voltage, thereby displaying the image. In this case, there may occur a difference in threshold voltage between the driving transistors of each pixel, which results in MURA of an image.
In order to solve such a problem, an internal compensation method and an external compensation method have been proposed. In the internal compensation method, a plurality of auxiliary transistors are further formed in each pixel so as to sample the threshold voltage of a driving transistor in the pixel and to compensate for the sampled threshold voltage. In the external compensation method, a second switching transistor applying a reference voltage is further provided, and a variation in the reference voltage applied by the second switching transistor is sensed, so as to compute a difference in threshold voltage between driving transistors through the sensed variation and to compensate for a data voltage.
In the internal compensation method, six thin film transistors including switching and driving transistors are provided in each pixel. Therefore, the configuration of a circuit is complicated, and an aperture ratio is decreased. On the other hand, in the external compensation method, each pixel can be implemented with no more than three thin film transistors, and it is possible to sense not only a difference in threshold voltage between driving transistors but also the amount of current flowing through the driving transistor. Thus, a variation in carrier mobility can also be computed, thereby maximizing compensation capability for a variation in element characteristic.
FIG. 1A is an equivalent circuit diagram of one pixel in a conventional organic light-emitting diode display device using an external compensation method. FIG. 1B is a waveform diagram illustrating waveforms of signals applied in driving of the pixel shown in FIG. 1A. FIG. 1C is a schematic diagram of the organic light-emitting diode display device using the external compensation method.
Referring FIG. 1A, the conventional organic light-emitting diode display device using the external compensation method includes an organic light-emitting diode D1, a driving transistor DR-T supplying current to the organic light-emitting diode D1, a first switching transistor SW-T1 connected between a data line and the driving transistor DR-T so as to apply a data voltage to a gate of the driving transistor DR-T according to a first scan signal Vscan, a second switching transistor SW-T2 connected between a reference voltage supply (not shown) and the driving transistor DR-T so as to apply a reference voltage to a source of the driving transistor DR-T according to a second scan signal Vscan2, and a capacitor C1 connected between the gate and source of the driving transistor DR-T.
According to the structure described above, if high-level first and second scan signals Vscan1 and Vscan2 are applied to each pixel, current flows through the first and second switching transistors SW-T1 and SW-T2 so that a data voltage Vdata is applied to the gate of the driving transistor DR-T, and a reference voltage Vref is applied to the source of the driving transistor DR-T, and a voltage of“VDD-|Vth|” and “Vdata” to both ends of the capacitor C1. Subsequently, if the voltage level of the first scan signal Vscan1 is changed into a low level and thus the first switching transistor SW-T1 is turned off, a voltage of “VDD−|Vth|−Vdata+Vref” is applied to the gate of the driving transistor DR-T, and as a result, the Ids of the driving transistor DR-T becomes “k(Vdata-Vref)2.” That is, a threshold voltage component is removed in the current flowing through the driving transistor DR-T, so that the current flowing through the driving transistor DR-T is controlled by the reference voltage Vref. Thus, a variation in element characteristic between pixels can be compensated by sensing current flowing through the driving transistor DR-T according to the variation (V0-V1) of the reference voltage Vref for a predetermined time t, computing a compensation value through the sensed current and reflecting the computed compensation value to the data voltage.
However, in the organic light-emitting diode display device using the external compensation method described above, as shown in FIG. 1C, a compensation circuit 40 for supplying and sensing the reference voltage Vref is further required in addition to a data driver 30 supplying the data voltage Vdata. Therefore, separate Integrated chips (ICs) are respectively provided to upper and lower portions of a display panel 10, which results in an increase in cost.
Although the external compensation method is applied to the organic light-emitting diode display device, the organic light-emitting diode display device is identical to that using the internal compensation method in that a plurality of signal lines such as a line for supplying the reference voltage Vref and a line for supplying power and ground voltages VDD and VSS are formed in the display panel 10. Accordingly, there is a limitation in improving an aperture ratio.